138 lines
7.1 KiB
HTML
138 lines
7.1 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- This file documents the GNU Assembler "as".
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Copyright (C) 1991-2016 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3
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or any later version published by the Free Software Foundation;
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with no Invariant Sections, with no Front-Cover Texts, and with no
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Back-Cover Texts. A copy of the license is included in the
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section entitled "GNU Free Documentation License".
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-->
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<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Using as: Bundle directives</title>
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<meta name="description" content="Using as: Bundle directives">
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<meta name="keywords" content="Using as: Bundle directives">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="AS-Index.html#AS-Index" rel="index" title="AS Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Pseudo-Ops.html#Pseudo-Ops" rel="up" title="Pseudo Ops">
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<link href="Byte.html#Byte" rel="next" title="Byte">
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<link href="Balign.html#Balign" rel="prev" title="Balign">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="Bundle-directives"></a>
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<div class="header">
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<p>
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Next: <a href="Byte.html#Byte" accesskey="n" rel="next">Byte</a>, Previous: <a href="Balign.html#Balign" accesskey="p" rel="prev">Balign</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Bundle-directives-1"></a>
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<h3 class="section">7.8 Bundle directives</h3>
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<a name="g_t_002ebundle_005falign_005fmode-abs_002dexpr"></a>
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<h4 class="subsection">7.8.1 <code>.bundle_align_mode <var>abs-expr</var></code></h4>
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<a name="index-bundle_005falign_005fmode-directive"></a>
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<a name="index-bundle"></a>
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<a name="index-instruction-bundle"></a>
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<a name="index-aligned-instruction-bundle"></a>
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<p><code>.bundle_align_mode</code> enables or disables <em>aligned instruction
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bundle</em> mode. In this mode, sequences of adjacent instructions are grouped
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into fixed-sized <em>bundles</em>. If the argument is zero, this mode is
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disabled (which is the default state). If the argument it not zero, it
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gives the size of an instruction bundle as a power of two (as for the
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<code>.p2align</code> directive, see <a href="P2align.html#P2align">P2align</a>).
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</p>
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<p>For some targets, it’s an ABI requirement that no instruction may span a
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certain aligned boundary. A <em>bundle</em> is simply a sequence of
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instructions that starts on an aligned boundary. For example, if
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<var>abs-expr</var> is <code>5</code> then the bundle size is 32, so each aligned
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chunk of 32 bytes is a bundle. When aligned instruction bundle mode is in
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effect, no single instruction may span a boundary between bundles. If an
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instruction would start too close to the end of a bundle for the length of
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that particular instruction to fit within the bundle, then the space at the
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end of that bundle is filled with no-op instructions so the instruction
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starts in the next bundle. As a corollary, it’s an error if any single
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instruction’s encoding is longer than the bundle size.
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</p>
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<a name="g_t_002ebundle_005flock-and-_002ebundle_005funlock"></a>
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<h4 class="subsection">7.8.2 <code>.bundle_lock</code> and <code>.bundle_unlock</code></h4>
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<a name="index-bundle_005flock-directive"></a>
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<a name="index-bundle_005funlock-directive"></a>
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<p>The <code>.bundle_lock</code> and directive <code>.bundle_unlock</code> directives
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allow explicit control over instruction bundle padding. These directives
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are only valid when <code>.bundle_align_mode</code> has been used to enable
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aligned instruction bundle mode. It’s an error if they appear when
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<code>.bundle_align_mode</code> has not been used at all, or when the last
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directive was <code><span class="nolinebreak">.bundle_align_mode</span> 0</code><!-- /@w -->.
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</p>
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<a name="index-bundle_002dlocked"></a>
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<p>For some targets, it’s an ABI requirement that certain instructions may
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appear only as part of specified permissible sequences of multiple
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instructions, all within the same bundle. A pair of <code>.bundle_lock</code>
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and <code>.bundle_unlock</code> directives define a <em>bundle-locked</em>
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instruction sequence. For purposes of aligned instruction bundle mode, a
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sequence starting with <code>.bundle_lock</code> and ending with
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<code>.bundle_unlock</code> is treated as a single instruction. That is, the
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entire sequence must fit into a single bundle and may not span a bundle
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boundary. If necessary, no-op instructions will be inserted before the
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first instruction of the sequence so that the whole sequence starts on an
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aligned bundle boundary. It’s an error if the sequence is longer than the
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bundle size.
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</p>
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<p>For convenience when using <code>.bundle_lock</code> and <code>.bundle_unlock</code>
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inside assembler macros (see <a href="Macro.html#Macro">Macro</a>), bundle-locked sequences may be
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nested. That is, a second <code>.bundle_lock</code> directive before the next
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<code>.bundle_unlock</code> directive has no effect except that it must be
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matched by another closing <code>.bundle_unlock</code> so that there is the
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same number of <code>.bundle_lock</code> and <code>.bundle_unlock</code> directives.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Byte.html#Byte" accesskey="n" rel="next">Byte</a>, Previous: <a href="Balign.html#Balign" accesskey="p" rel="prev">Balign</a>, Up: <a href="Pseudo-Ops.html#Pseudo-Ops" accesskey="u" rel="up">Pseudo Ops</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="AS-Index.html#AS-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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